Electron-impact collision strengths and rate coefficients for W vii - applications in fusion plasma modelling

Abstract

Currently, Tungsten (W) remains one of the most important materials used in plasma facing components (PFCs) in tokamaks in regards to the construction of divertors and first wall materials. Plasma modelling, including erosion and transport studies, are hindered by the lack of comprehensive atomic data sets available, especially for the atomic structure and excitation rate coefficients. This paper presents a Multi-Configurational Dirac–Fock (MCDF) approach to the atomic structure of W VII which is the foundation of a subsequent Dirac Atomic R-Matrix Calculation (DARC) for electron-impact excitation. The collision calculations initially produce collision strengths for a wide range of incident electron energies, which are then Maxwellian convolved to produce effective collision strengths across a range of relevant temperatures. Derived transition rates from the atomic structure and excitation rates from the collisional evaluations form the basis of a collisional-radiative model to calculate Photon Emmisivity Coefficients (PECs) under a variety of pertinent electron temperatures and densities. The resulting synthetic spectra are compared with measured spectra taken at the Joint European Torus (JET) experiment and very good agreement is found for some diagnostically significant transitions.